Apparatus for recording oscilloscopic signal traces



R. E. MCCORMICK oct. 31, 195o APPARATUS FOR RECORDING OSCILLOSCOPIC SIGNAL TRACES med Aug. 2, 1945 3 Sheets-Sheet 1 WNM P HM umwwwm Tfnuj a 1111111 r -Nn u M A sifwr Hilllllfiflll M H HH huwuuh .WH mi y 'ma/@wif MM Arme/VU Oct. 3l, 1950 R. E. MCCORMICK APPARATUS FOR RECORDING OSCILLOSCOPIC SIGNAL TRACES 3 Sheets-Sheet 2 Filed Aug.` 2, 1945 wrm/me Arm/@vir I' 1 Oct. 3l, 1950 R, E, MocoRMlK l 2,527,562

APPARATUS FOR RECORDING oscILLoscoPIc SIGNAL TRAcEs Filed Aug. 2, 1945 y :s sheets-sheet 3 Patented Oct. 31, 195'() UNITED STATES PATENT OFFICE APPARATUS FOR RECORDING OSCILLO- SCOPIC SIGNAL TRACES 2 Claims.

amended April 30, 1928; 370 O. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to improvements in recording devices and particularly is a novel means for photographing effectively wave traces appearing on the screen of a cathode ray oscilloscope.

The recorder is susceptible of many applications in laboratory and eld; examples are' the check'- ing and comparison of all types of wave forms (pulses, sine waves, and square waves), examination of relay operation (timing and cleanness of the operation and closing of contacts), and examination of the characteristics and operation of continuous wave transmitters (keying, frequency stability and the like).

One object of this invention is to vprovide a means for producing an accurate photographic record of the output of a cathode ray tube.

Another object is to provide oscilloscopio cir-v cuits which will cause visual wave traces, suitable for photographing, to be projected on the cathode ray tube screen.

Additional objects will be apparent from a readingof `the following specification and claims.

In the drawings:

Figure 1 is a perspective view, partly cut away, of the oscilloscopio recorder of my invention.

Figure 2 illustrates the means by which the cathode ray tube image is focused on a nlm or other sensitized surface.

Figure 3 illustrates a means for supplying signals of various types to a cathode ray tube.

Figure 4 is a perspective view of the means for driving the drum utilized in 'the invention past the image focusing means.

Figure 5 is a detail in perspective of one end of the carriage which carries the drum.

Figure 6 represents a sample lm with oscilloscope tracings thereon.

Generally speaking, the device comprises a lens system and a sensitized film which is mounted upon a drum which rotates ata constant speed and which is driven axiallylikewise at a constant speed. e

The revolving drum assembly comprises a, drum proper I adapted to carry a film or sensitized paper, a carriage II which supports the drum, a motor I2 for rotating the same, and tracks I3 and I4 upon which the carriage moves on wheels, as I and I6. A cover must be provided to keep stray light from the lm or sensitized paper, but this cover does not appear in the drawings.

2 Tracks I3' andr I4 are so located with respectfto a cathode ray tube oscilloscope 20 that thecarfriage II and the drum I Will move parallel to and adjacent the oscillograph screen. y v

A trace appearing on the screen of the oscilloscope 20 is cast upon sensitized paper or ,lm carried by the drum I0 through the lens 2| fixedy in a tube 22 for movement toward and away from the oscilloscope 2U. providesfor proper focusing of the image. Focus' may be maintained by tightening thesetscrew 23, The sensitized paper may be shielded from the cathode ray tube by means of a lightproof shutter 24 which moves in grooves 24 and 24" in front of the screen. l

Beneath the carriage II and forming a part thereof is a rack 25 which cooperates with a pinion 26 and a shaft 2'I (see Figure 4). This shaft is driven by a second motor 28 which produces rotation through suitable gearing 29 and 30 of the shaft 21. The speed at which the shaft 2"I is `to be driven and .thus the ratio between the gears 2d and 3l? depends upon the requirements of ,the apparatus, but the speed of the carriage may well be of the order of five eighths inch per second.

rlwo switches are utilized to control the vtravel of carriage II. A suitable switch 3l Ais shown in Figure 5. As long as the camming surface 32 of, carriage II bears upon the wheel 33 of switch beyond the switch, the said contacts are opened,

and motor '28 is stopped. f Preferably, one suchv switching means stops the carriage at about the midpoint of its travel; another, at the end, ofy

its travel.

In" the embodiment shown, carriage: II is.

adapted to be moved manually back to its start-` ing point after being stopped. This is accomplished by moving a lever 34 against a pin. 35,

thereby to move the slide 35 beneath a pin 36,. secured to the housing of motor 28. The housing, is hinged at 37 along one of its edges-(at the, The motor 28, with its h0us;

The movement of lens" fier of any conventional type, the output of which may be applied directly across the horizontal deflecting plates.

The other portion of Figure 3 is utilized to show frequency deviations in the signal being studied. Input to the circuit is from amplier 40, through switches 42 and 43, and contacts 42 and 43' respectively. The circuit includes a limiter 46 in which plate saturation occurs at a low predetermined level so that signal amplitude increases beyond this level do not aifect the plate current. The output of the limiter is passed through an amplifier 47 which is transformer coupled to a dscrirninator circuit 48. The transformer has a tuned primary and secondary with a coeflicient of coupling determined by the width of the band of frequencies it is desired to pass.

The voltage applied to rectier 5G consists of two components, that fed into the center of the secondary winding of transformer 5I, and that induced in the secondary. The phase relationship' between the two is such that at resonance the'cu'rrents are equal in value but iiow in oppsit'e directions in resistors 52 and 53 so that the riet voltage across the horizontal deflecting plates of oscilloscope is zero under these conditions. When the carrier deviates from resonance, the induced secondary current either lags orv leads depending upon whether deviation is to the high side or to the low side of resonance,

and this phase shift causes the inducedcurrent to combine with that fed into the secondary winding of transformer 5l in such a way that the output of one half of rectifier 5o is higher than that of the other. A voltage which represents the difference between the outputs of the two vhalves of rectifier 59 is amplied at 52 and applied across the horizontal deflecting plates of oscilloscope 20. 'Io record a representation of a desired signal, the signal is applied to the amplifier 40, Figure 3, and directly to oscilloscope 20 or, after proper manipulation of switches 42 and 43, through amplifier and the frequency modula tion section of the oscilloscope control. At no signal, the cathode ray will be focused at the vertical center of the tube, since the vertical deflecting plates are grounded. As the signal to be recorded is applied across the deflecting plates, the cathode ray is deected proportionately.

Lens 2| is adjusted to provide an image of the desired size, preferably on the order of a quarter inch, and secured by tightening the screw 23. Film is'put upon drum I0, and motors l2 and 28 started, and, as the drum revolves and moves across the end of tube 22, the oscilloscopio trace is recorded on the film. When the drum assembly h as reached the midpoint of its travel, switch 33 isactuate'd by lug 32 and brings the assembly tov a halt. The drum assembly may then be moved manually back to its starting position, as explained, rotatory motion of the drum (which results in a spiral recording path) assuring that a new recording will not be superimposed upon the rst.

` The rotating drum forms a mechanical sweep circuit taking the place of the electrical sweep used in a standard oscilliscope, the screen of which is intended to be viewed instead of photographed.

Because the drum is driven by a motor which is supplied from a constant frequency source, time measurements may be made directly on the lm without the need for superimposing a time base.

Figure 6 requires no extended explanation, it being included merely to show the appearance of a completed record made by the present invention. The tracings are made normally column by column; the regularity of the record and the ease of comparison are readily apparent.

The foregoing description is in specific terms, but, since many modifications obviously can be made without departing from the spirit of the invention, it should not be construed as limiting the invention otherwise than in the light of the appended claims.

I claim:

1. In an apparatus of the nature described, the combination of means for projecting an oscilloscopio trace or the like, a track arranged before said projecting means in spaced relation thereto, a carriage mounted on said track for movement thereon relative to said projecting means, a rotatable drum on said carriage for carrying a recording medium, means for focusing said trace upon said dmm, means for rotating said drum, a rack secured to said carriage parallel to said track, a pinion engaged with said rack and adapted when rotated to drive said rack and said carriage along said track, and means including a motor for rotating said pinion said last-mentioned means being disengageable from said pinion and when disengaged permitting manually controlled movement of said carriage upon said track.

2. The invention of claim l, further characterized in that said last-mentioned means includes a support forsaid motor hinged along one of its edges whereby the support and motor may be rotatably lifted upon said hinge.

RAYMOND E. MCCORMICK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 957,257 Robinson May 10, 1910 1,864,363 McCreary June 21, 1932 1,977,453 Petit et al. Oct. 16, 1934 2,123,151 Petit et al. July 5, 1938 2,153,140 Diehl Apr. 4, 1939 2,186,268 Pakala Jan. 9, 1940 2,241,432 Von Ardenne et al. May 13, 1941 2,307,5054 HeinmetsQ Jan. 5, 1943 2,394,435 Finch Feb. 5, 1946 FOREIGN PATENTS Number Country Date 28,601 Great Britain 1913 OTHER REFERENCES Journal of Scientific Instruments, vol 14, 1937, pages 209 to 212. 

